Opacifying pigment particle

ABSTRACT

An opacifying pigment that includes a pigment particle having an average particle diameter of from 0.005 to 5 microns and an index of refraction of at least 1.8 such as, for example TiO2, at least partially encapsulated in polymer is provided. Also provided are processes for forming the encapsulated pigment particle and compositions including the encapsulated pigment particle.

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Patent Application Nos. 61/216,584 filed on May 19,2009 and 61/340,071 filed on Mar. 12, 2010.

This invention relates to an opacifying pigment particle encapsulated inpolymer. More specifically, the invention relates to an opacifyingpigment encapsulated in polymer including a pigment particle having anaverage particle diameter of from 0.005 to 5 microns and an index ofrefraction of at least 1.8; from 0.1% to 25% by weight, based on theweight of the pigment particle, water-soluble sulfur acid-functionalfirst polymer; and from 10% to 200%, by weight, based on the weight ofthe pigment particle, second polymer that at least partiallyencapsulates the pigment particle. The invention also relates to aprocess for forming the opacifying pigment encapsulated in polymer andcompositions including the opacifying pigment encapsulated in polymer.

Opacifying pigments provide whiteness, and opacity or “hiding”, toopacifying coatings, such as paints, and to plastics. These pigments arepresent in most coatings that are designed to provide an opaque coatingon and to concealingly cover an undersurface or substrate surface towhich the coating is applied. These pigments are also present in mostplastics that are designed to be totally or partially opaque. In paintsand plastics, an opacifying pigment is present whether the paint iswhite or colored. It is often desirable that opacifying coatings,paints, and plastics have a high opacifying efficiency so as to enablethe coating or paint to completely conceal the undersurface, even if itis of a sharply contrasting color, while utilizing a minimal thicknessof the coating or paint, or plastic.

Opacifying coating, paint, and plastics manufacturers have long soughtto formulate opacifying coating, paints, and plastics having a desiredopacity by maximizing the level of hiding while minimizing the amount ofopacifying pigment utilized. Without being bound by a particular theory,it is believed that opacifying effectiveness is a function of thespacing between the particles of opacifying pigment in the coating orplastic. Maximum light scattering efficiency occurs when the opacifyingpigment particles have a certain diameter and spacing, so that the lightscattering capability of each particle does not interfere with the lightscattering capability of its neighboring particles. This condition mayoccur in coatings and plastics containing sufficiently low levels ofopacifying pigment such that the individual opacifying pigment particlesare isolated from each other. Coatings and plastics containing such lowlevels of opacifying pigment, however, often do not provide sufficientopacity or hiding at a desirable thicknesses. Achieving the desiredlevels of hiding or opacity typically requires higher levels ofopacifying pigment. At these higher levels, a statistical distributionof opacifying pigment particles occurs, which results in at least someof the opacifying pigment particles being in such close proximity to oneanother that there is a loss of light scattering efficiency due tocrowding of the opacifying pigment particles. Increased hidingefficiency is obtained by reducing the crowding of the opacifyingpigment particles and minimizing the formation of clusters of opacifyingpigment particles. One method to achieve this is to encapsulate theopacifying pigment particles within a polymer matrix by polymerizingpolymer on the surface of the opacifying pigment particles.

U.S. Pat. No. 4,421,660 discloses inorganic solids encapsulated in apolymer matrix, wherein the inorganic solids are encapsulated in ahydrophobic addition polymer by a polymerization process wherein awater-immiscible monomer is dispersed in an aqueous colloidal dispersionof the inorganic particles polymer by an emulsion polymerizationprocess. Prior to the emulsion polymerization process, the pigmentparticles are dispersed in water using dispersants or surfactants.Although this process is described as providing pigment particlesencapsulated in a polymeric material, the disclosed process employingthe disclosed dispersants and surfactants produces large amounts of gel,and is not viable.

We have discovered that certain sulfur acid-functional polymers, whenused as dispersants for certain inorganic pigment particles, provide forthe encapsulation of the pigment particles via a viable emulsionpolymerization process. The opacifying pigment encapsulated in polymerprovides desirably high hiding efficiency and is capable of being formedin an aqueous medium with low grit levels.

According to a first aspect of the present invention there is providedan opacifying pigment encapsulated in polymer comprising: a pigmentparticle having an average particle diameter of from 0.005 to 5 micronsand an index of refraction of at least 1.8; from 0.1% to 25% by weight,based on the weight of said pigment particle, water-soluble sulfuracid-functional first polymer; and from 10% to 200%, by weight, based onthe weight of said pigment particle, second polymer that at leastpartially encapsulates said pigment particle.

According to a second aspect of the present invention there is provideda process for forming an opacifying pigment encapsulated in polymercomprising: (a) dispersing a pigment particle having an average particlediameter of from 0.005 to 5 microns and an index of refraction of atleast 1.8 in a medium with from 0.1% to 25% by weight, based on theweight of said pigment particle, water-soluble sulfur acid-functionalfirst polymer; and (b) performing an emulsion polymerization in thepresence of said dispersed pigment particle to provide from 10% to 200%,by weight, based on the weight of said pigment particle, second polymerthat at least partially encapsulates said dispersed pigment particle.

According to a third aspect of the present invention there is provided acomposition comprising said opacifying pigment encapsulated in polymerformed by the process of the second aspect of the present invention.

The present invention relates to an opacifying pigment encapsulated inpolymer. The opacifying pigment particle has an average particlediameter of from 0.005 to 5 microns and an index of refraction of atleast 1.8. By “opacifying” herein is meant that the particle engendersopacity when subject to light of a certain wavelength, not necessarilyvisible light. For example certain nano-particles included hereinprovide opacity when subject to light of wavelengths lower than thevisible range. The shape of the pigment particles is not important.Suitable shapes for the pigment particles include spherical shapes, suchas a regular sphere, an oblate sphere, a prolate sphere, and anirregular sphere; cubic shapes such as a regular cube and a rhombus;plate-like shapes including a flat plate, a concave plate, and a convexplate; and irregular shapes. The pigment particles having sphericalshapes have average diameters in the range of from 5 nm to 5 micron,preferably in the range of from 150 nm to 500 nm, and more preferably,in the range of from 200 nm to 350 nm. Pigment particles havingnonspherical shapes preferably have average diameters, defined as theirmaximum dimension, of from 5 nm to 5 micron, more preferably of from 150nm to 500 nm, and most preferably of from 200 nm to 350 nm. The averagediameters of pigment particles are typically provided by pigmentparticle suppliers.

The pigment particles are also characterized as having an index ofrefraction [n_(D) (20° C.)] that is at least 1.8, preferably at least1.9, and more preferably at least 2.0. The indices of refraction forvarious materials are listed in CRC Handbook of Chemistry and Physics,80th Edition, D. R. Lide, editor, CRC Press, Boca Raton, Fla., 1999,pages 4-139 to 4-146.

Suitable opacifying pigment particles include zinc oxide, antimonyoxide, zirconium oxide, chromium oxide, iron oxide, lead oxide, zincsulfide, lithopone, and forms of titanium dioxide such as anatase andrutile. Preferably, the pigment particles are selected from titaniumdioxide and lead oxide. More preferably, the pigment particles areselected from rutile titanium dioxide and anatase titanium dioxide. Mostpreferably, the pigment particles are rutile titanium dioxide. A coatingcontaining two different forms of a material, such as rutile and anatasetitanium dioxide, is considered to have two different pigments.

The pigment particles may have a uniform composition or a heterogeneouscomposition with two or more phases. Certain heterogeneous pigmentparticles have an inner core and surrounding shell structure wherein onetype of pigment particle forms the core and another type of particleforms the shell. The core and shell heterogeneous pigment particlesinclude core/shell particles having a shell completely or incompletelyencapsulating the core; core/shell particles having more than one core;dipolar particles; and particles having multiple domains of one phase onthe surface of the other phase. Pigment particles, such as titaniumdioxide, can have at least one coating of one or more of silica,alumina, zinc oxide, and zirconia. For example, in certain embodimentstitanium dioxide particles suitable for use in coatings of the presentinvention may have a coating of silica and a coating of alumina.

In the first aspect of the invention the opacifying pigment encapsulatedin polymer includes from 0.1% to 25%, preferably from 0.25% to 10%, morepreferably from 0.5% to 5%, and most preferably from 0.5% to 2% byweight, based on the weight of the pigment particle, water-solublesulfur acid-functional first polymer. Typically the pigment particleshave been dispersed in a medium, preferably an aqueous medium, with thewater-soluble sulfur acid-functional first polymer. By “aqueous medium”herein is meant water and from 0 to 30%, by wt. based on the weight ofthe aqueous medium, of water-miscible compound(s). “Sulfuracid-functional polymer” herein includes any water-soluble polymerincluding at least three sulfur acid moieties. As used herein, the term“sulfur acid-functional monomer” is meant to include any monomercontaining at least one free radical polymerizable vinyl group, and atleast one sulfur acid moiety. As used herein, the term “sulfur acidmoiety” is meant to include any of the following residues: —S(O)2(OH),—OS(O)2(OH), —OS(O)(OH), —S(O)(OH). Also included in the definition ofterm “sulfur acid moiety” are salts of the above residues. As usedherein, the term “water-soluble sulfur acid-functional first polymer”means that the sulfur acid-functional first polymer is soluble in waterat 25° C. at a pH of less than or equal to 5 to an extent of at least 5%by weight.

The sulfur acid-functional first polymer can be any of a polymer with atleast three sulfur acid moieties located randomly in the polymerbackbone, a block copolymer with a single sulfur acid-including blockand at least one block which does not have sulfur acids, or a comb-graftpolymer with a backbone that includes sulfur acids and teeth which donot include sulfur acids. The block copolymers can have the sulfuracid-including block located terminal to the polymer, or within theinterior of the polymer chain. In a preferred embodiment of the presentinvention, the sulfur acid-functional polymer contains both sulfur acidand amine moieties. In this preferred embodiment of the presentinvention, it is further preferred that the polymer have at least twoamine and three sulfur acid groups, it is more preferred that thepolymer have at least three amine and five sulfur acid groups, it ismost preferred that the polymer have at least four amine and eightsulfur acid groups. The number of amine and sulfur acid groups may bethe same or different. It is preferred that the ratio of amine to sulfuracid groups be between 10:1 and 1:10, more preferred that the ratio ofamine to sulfur acid groups be between 3:1 and 1:4, most preferred thatthe ratio of amine to sulfur acid groups be between 1.5:1 and 1:3, on amolar basis. The sulfur acid-functional polymer may be made as asolution polymer in water or a non-aqueous solvent, or as a bulkpolymer. The sulfur acid-functional polymer may be made by any suitablepolymerization process, such as addition polymerization of ethylenicallyunsaturated monomers such as acrylic, styrenic, or vinyl monomers.Polymers that contain both amine and sulfur acid groups may be made bycopolymerizing at least one amine-functional monomer and at least onesulfur acid-functional monomer, or they may be made by including atleast one monomer which is both amine-functional and sulfuracid-functional in the monomer mix. As a further example, polymers thatinclude both amine and sulfur acid groups may be made by the additionpolymerization of ethylenically unsaturated monomers, including in themonomer mix functional monomers that can be converted to amine or sulfuracid groups after the polymerization is completed. Examples of monomersthat can be converted to amines after the polymerization is completedinclude isocyanate-functional monomers, which can be reacted withprimary-tertiary or secondary-tertiary diamines, epoxy-functionalmonomers that can be reacted with amines, andhalomethylbenzyl-functional monomers that can be reacted with amines.Examples of monomers that can be converted to sulfur acids after thepolymerization is completed include isocyanate-functional monomers,which can be reacted with aminosulfates. Block copolymers that include asulfur acid-functional polymer-including block may be made by any knownprocess that is capable of producing such polymers. For example, blockcopolymers that include a sulfur acid-functional polymer-including blockmay be made by the living free radical polymerization of ethylenicallyunsaturated monomers wherein the monomer composition of one of themonomer feeds includes at least one sulfur acid-functional unsaturatedmonomer. As a further example, block copolymers that include a sulfuracid-functional polymer-including block may be made by the living freeradical polymerization of ethylenically unsaturated monomers, includingin the monomer mix functional monomers that can be converted to sulfuracid groups after the polymerization is completed. Comb-graft polymersthat include a sulfur acid-functional polymer-including backbone may bemade by any known process that is capable of producing such polymers.For example, comb-graft polymers that include a sulfur acid-functionalpolymer-including backbone may be made by the free radicalpolymerization of ethylenically unsaturated monomers wherein the monomercomposition includes at least unsaturated macromer and at least onesulfur acid-functional unsaturated monomer. As a further example,comb-graft polymers that include a sulfur acid-functionalpolymer-including backbone may be made by the living free radicalpolymerization of ethylenically unsaturated monomers, including in themonomer mix functional monomers that can be converted to sulfur acidgroups after the polymerization is completed. It is preferred that thesulfur acid-functional polymer be a linear random copolymer.

The sulfur acid-functional polymer is typically prepared by the additionpolymerization of ethylenically unsaturated monomers. Suitable monomersinclude styrene, butadiene, alpha-methyl styrene, vinyl toluene, vinylnaphthalene, ethylene, propylene, vinyl acetate, vinyl versatate, vinylchloride, vinylidene chloride, acrylonitrile, methacrylonitrile,(meth)acrylamide, various C1-C40 alkyl esters of (meth)acrylic acid; forexample, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate,n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl(meth)acrylate, tetradecyl (meth)acrylate, lauryl (meth)acrylate, oleyl(meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate;other (meth)acrylates such as isobornyl (meth)acrylate, benzyl(meth)acrylate, phenyl (meth)acrylate, 2-bromoethyl (meth)acrylate,2-phenylethyl (meth)acrylate, and 1-naphthyl (meth)acrylate, alkoxyalkyl(meth)acrylate, such as ethoxyethyl (meth)acrylate, mono-, di-, trialkylesters of ethylenically unsaturated di- and tricarboxylic acids andanhydrides, such as ethyl maleate, dimethyl fumarate, trimethylaconitate, and ethyl methyl itaconate; alcohol containing monomers suchas hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate,hydroxybutyl (meth)acrylate; carboxylic acid containing monomers, suchas (meth)acrylic acid, itaconic acid, fumaric acid, and maleic acid.Examples of suitable sulfur acid-functional monomers include sulfoethyl(meth)acrylate, sulfopropyl (meth)acrylate, styrene sulfonic acid, vinylsulfonic acid, and 2-(meth)acrylamido-2-methyl propanesulfonic acid, andsalts there of. Examples of suitable amine-functional monomers includedimethylamino ethyl(meth)acrylate, dimethylamino propyl(meth)acrylamide,and t-butylamino ethyl(meth)acrylate. As used herein, the term“(meth)acrylate” refers to either acrylate or methacrylate and the term“(meth)acrylic” refers to either acrylic or methacrylic.

The sulfur acid-functional polymer random copolymer, sulfur acidincluding block of the block copolymer, or sulfur acid includingbackbone of the comb-graft polymer may have a weight average molecularweight of 1000 to 200,000, preferably from 1000 to 50,000, morepreferably from 2000 to 15,000, and most preferably from 3000 to 10,000.When the sulfur acid-functional polymer is a block copolymer or acomb-graft polymer, the non-sulfur acid including block(s) or teeth,respectively, may have a weight average molecular weight of 750 to200,000, more preferably from 1000 to 50,000, more preferably form 1500to 25,000, and most preferably from 5000 to 15,000. The molecularweights may be determined by GPC.

The pigment particles may be dispersed in an aqueous medium with thewater-soluble sulfur acid-functional polymer. The sulfur acid-functionalpolymer can be made water-soluble by the inclusion of sufficient amineand or sulfur acid groups, as well as by including sufficient levels ofcopolymerized water-soluble monomers such as alcohol-functional monomerssuch as hydroxyethyl (meth)acrylate; amide-functional monomers such as(meth)acrylamide; acid-functional monomers such as (meth)acrylic acid;or combinations thereof. The levels of water-soluble monomers necessaryto render the sulfur acid-functional polymer or polymer block or teethwater-soluble will depend on the molecular weight and nature of theco-monomers included in the composition of the sulfur acid-functionalpolymer, blocks, or teeth, as is known in the art. When the sulfuracid-functional polymer is a block copolymer or a comb-graph polymer, itis preferred that the non-sulfur acid block(s) or teeth, respectively,be in themselves water-soluble.

The opacifying pigment encapsulated in polymer of the present inventionincludes from 10% to 200%, by weight, based on the weight of the pigmentparticle, second polymer that at least partially encapsulates thepigment particle. The second polymer is typically prepared by freeradical emulsion polymerization of ethylenically unsaturated monomers inthe presence of the pigment particle that has been dispersed in amedium. In some embodiments the second polymer is made of a monomermixture containing at least one water-soluble monomer. Examples ofsuitable water soluble monomers are acid functional monomers like2-sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, styrenesulfonic acid, vinyl sulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, acrylic acid, methacrylic acid, itaconic acid andthe salts thereof. Other suitable water soluble monomers are acrylamide,diacetoneacrylamide, 2-hydroxyethyl methacrylate and 2-hydroxyethylacrylate.

By “at least partially encapsulated” herein is meant that the secondpolymer is in contact with at least a part of the surface of the pigmentparticle. The degree of encapsulation of the pigment particle may bedetermined using an electron micrograph. Determination of the degree ofencapsulation does not include any contribution of first polymer,surfactant, dispersant, or the like. By “X % encapsulated” herein ismeant that X % of the surface area of the pigment particle is in contactwith the second polymer; preferably greater than 50%, more preferablygreater than 75%, and most preferably 100% of the surface area of theparticle is in contact with the second polymer. The thickness of thesecond polymer encapsulant layer or shell may be up to 500 nm; for TiO2pigment, for example, preferred thickness of the second polymerencapsulant layer or shell is typically between 20 nm and 150 nm,preferably from 40 nm to 100 nm.

In an aspect of the present invention the process for forming anopacifying pigment encapsulated in polymer includes: (a) dispersing apigment particle having an average particle diameter of from 0.005 to 5microns and an index of refraction of at least 1.8 in a medium with from0.1% to 25% by weight, based on the weight of the pigment particle,water-soluble sulfur acid-functional first polymer; and (b) performingan emulsion polymerization in the presence of the dispersed pigmentparticle to provide from 10% to 200%, by weight, based on the weight ofsaid pigment particle, second polymer that at least partiallyencapsulates said dispersed pigment particle.

A step in this process of the present invention consists of dispersingopacifying pigment particles in a medium, preferably an aqueous medium,with a water-soluble sulfur acid-functional polymer. This dispersionstep may be effected by any means commonly used to disperse pigments inan aqueous medium, including, for example, grinding with a high speeddispersator, or grinding in media mills or ball mills. The weight of thewater-soluble sulfur acid-functional polymer based on the weight of thepigment particles can range from 0.1% to 25%, preferably from 0.25% to10%, more preferably from 0.5% to 5%, and most preferably from 0.5% to2%.

In any event the opacifying pigment dispersion must have sufficientstability during storage (substantially maintaining the same particlesize, no or minimal sediment formation) and must have sufficientstability to withstand flocculation during the second polymerencapsulation process. During the initial stages of the encapsulationprocess the stabilization mechanism will typically change from adispersant-stabilized particle surface at a first pH to asurfactant-stabilized polymer surface at a lower pH. It is believed thatwhile this change is taking place there will inevitably be an intervalin which the stabilization by the dispersant is reduced and if thestabilization gets too weak then flocculation of TiO₂ particles willoccur.

A step in the process of the present invention includes at leastpartially encapsulating the dispersed pigment particles with from 10% to200%, by weight, based on the weight of the pigment particle, secondpolymer by performing an emulsion polymerization in the presence of thedispersed pigment particles. Alternatively, it is contemplated that thedispersion of polymer particles may be dried or partially dried andredispersed in an aqueous medium prior to encapsulation.

The emulsion polymerization can be carried out by methods well known inthe polymer art, and includes multiple stage polymerization processes.Various synthesis adjuvants such as initiators, chain transfer agents,and surfactants are optionally utilized in the polymerization. Ingeneral, the emulsion polymerization is of a seeded type emulsionpolymerization, with the dispersed pigment particles acting as theseeds. In one embodiment of the present invention, the reaction vesselis charged with water, dispersed pigment, and optionally surfactants andother polymerization adjuvants, and then the monomers for the secondpolymer are added to the kettle. In another embodiment of the presentinvention, the reaction vessel is charged with water, dispersed pigment,and optionally surfactants and other polymerization adjuvants, and thena part of the monomers for the polymer matrix is added to the kettle,and then a seed consisting of emulsified polymer particles, madeseparately, is added, and finally the remainder of the monomer for thepolymer matrix is added to the kettle. In yet another embodiment of thepresent invention, the reaction vessel is charged with water, andoptionally surfactants and other polymerization adjuvants and optionallya polymer seed, then a part of the monomers for the polymer matrix isadded to the kettle, then the dispersed pigment is added to the kettle,and finally the remainder of the monomer for the polymer matrix is addedto the kettle. The polymerization may be run as a shot process, or byusing multiple shots, or by continuously feeding in the monomer overtime. The monomer may be added neat or emulsified in water withappropriate surfactants. For the process to be considered acceptableherein it must be capable of being effected at a final volume solidslevel of 40 vol % or higher, preferably at 45 vol %, with less than 1.0%by weight, based on the weight of total solids, of grit formation.

In a preferred embodiment of the present invention, the second polymerincludes at least one sulfur acid-functional monomer. Examples ofsuitable sulfur acid-functional monomers include sulfoethyl(meth)acrylate, sulfopropyl (meth)acrylate, styrene sulfonic acid, vinylsulfonic acid, and 2-(meth)acrylamido-2-methyl propanesulfonic acid, andsalts thereof. Preferably the sulfur acid-functional monomer is styrenesulfonic acid or its salt. The sulfur acid-functional monomer may bepresent at a level of from 0.1% to 20% by weight of the monomers used tomake the second polymer containing the sulfur acid-functional monomer,preferably from 0.25% to 10%, more preferably from 0.25% to 5%, mostpreferably from 0.5% to 2%. If the second polymer contains more than onepolymer phase, then the sulfur acid-functional monomer may be present injust some or in all of the polymer phases. If the second polymercontains more than one polymer phase, it is preferable that the sulfuracid-functional monomer is present in the first polymer stage to bepolymerized.

Polymerization of the monomers for the second polymer is effected byaddition of a polymerization initiator. The polymerization initiator maybe added to the kettle prior to the monomer addition, or concurrent withthe monomer addition, after the monomer addition, or as a combination ofthese. Examples of suitable polymerization initiators includepolymerization initiators that thermally decompose at the polymerizationtemperature to generate free radicals. Examples include bothwater-soluble and water-insoluble species. Examples of suitable freeradical-generating initiators include persulfates, such as ammonium andalkali metal (potassium, sodium, and lithium) persulfate; azo compounds,such as 2,2′-azobis(isobutyronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), and t-butyl azocyanocyclohexane;hydroperoxides, such as t-butyl hydroperoxide and cumene hydroperoxide;peroxides, such as benzoyl peroxide, caprylyl peroxide, di-t-butylperoxide, ethyl 3,3′-di-(t-butylperoxy) butyrate, ethyl3,3′-di(t-amulperoxy) butyrate, t-amylperoxy-2-ethyl hexanoate, andt-butylperoxy pivilate; peresters, such as t-butyl peracetate, t-butylperphthalate, and t-butyl perbenzoate; as well as percarbonates, such asdi(1-cyano-1-methylethyl)peroxy dicarbonate; and perphosphates.

Polymerization initiators may be used alone, and alternatively, as theoxidizing component of a redox system, which also includes a reducingcomponent, such as an acid selected from the group consisting of:ascorbic acid, malic acid, glycolic acid, oxalic acid, lactic acid, andthioglycolic acid; an alkali metal sulfite, typically a hydrosulfite,such as sodium hydrosulfite; a hyposulfite, such as potassiumhyposulfite; or a metabisulfite, such as potassium metabisulfite; andsodium formaldehyde sulfoxylate.

Suitable levels of initiator and the optional reducing component includeproportions of from 0.001% to 5% each, based on the weight of themonomers in the monomer mixture to be polymerized. Accelerators such aschloride and sulfate salts of cobalt, iron, nickel, and copper aregenerally used in small amounts. Examples of redox catalyst systemsinclude t-butyl hydroperoxide/sodium formaldehyde sulfoxylate/Fe(II),and ammonium persulfate/sodium bisulfite/sodium hydrosulfite/Fe(II).

Chain transfer agents are optionally added to the aqueous reactionmedium to control molecular weight of the second polymer. Examples ofchain transfer agents include mercaptans, polymercaptans, andpolyhalogen compounds. Examples of suitable chain transfer agentsinclude alkyl mercaptans, such as ethyl mercaptan, n-propyl mercaptan,n-butyl mercaptan, isobutyl mercaptan, t-amyl mercaptan, n-hexylmercaptan, cyclohexyl mercaptan, n-octyl mercaptan, n-decyl mercaptan,n-dodecyl mercaptan; 3-mercaptoproprionic acid; 2-hydroxyethylmercaptan; alcohols, such as isopropanol, isobutanol, lauryl alcohol,and t-octyl alcohol; and halogenated compounds, such as carbontetrachloride, tetrachloroethylene, and trichlorobromoethane. Generallyfrom 0 to 10% chain transfer agent, by weight based on the weight of themonomer, is used to prepare the second polymer. Other techniques forcontrolling molecular weight, known in the art, include selecting theratio of the initiator to total monomer amount.

Catalyst and/or chain transfer agent are optionally dissolved ordispersed in separate or the same fluid medium, and gradually added tothe polymerization vessel. Monomer, neat, dissolved, or dispersed in afluid medium, is optionally added simultaneously with the catalystand/or the chain transfer agent.

The emulsion polymerization reaction medium typically containssurfactant to stabilize the growing second polymer-encapsulatedparticles during polymerization and to discourage aggregation of thepolymer-encapsulated pigment particles in the resulting aqueousdispersion. One or more surfactants, including anionic and nonionicsurfactants, and mixtures thereof, are commonly used. Many examples ofsurfactants suitable for emulsion polymerization are given inMcCutcheon's Detergents and Emulsifiers (MC Publishing Co. Glen Rock,NF), published annually. Other types of stabilizing agents, such asprotective colloids, are optionally used. However, it is preferred thatthe amount and type of stabilizing surfactant or other type ofstabilizing agent employed during the polymerization reaction beselected so that residual stabilizing agent in the resulting aqueousdispersion does not significantly interfere with the properties of theaqueous dispersion, the properties of compositions including the aqueousdispersion, or articles prepared from the aqueous dispersion.

Suitable anionic surfactants include, for example, alkali fatty alcoholsulfates, such as sodium lauryl sulfate; arylalkyl sulfonates, such aspotassium isopropylbenzene sulfonate; alkali alkyl sulfosuccinates, suchas sodium octyl sulfosuccinate; and alkali arylalkylpolyethoxyethanolsulfates or sulfonates, such as sodium octyl phenoxypolyethoxyethylsulfate, having 1 to 5 oxyethylene units.

Suitable nonionic surfactants include, for example, alkylphenoxypolyethoxy ethanols having alkyl groups of from 7 to 18 carbonatoms and from 6 to 60 oxyethylene units, such as, for example, heptylphenoxypolyethoxyethanols; ethylene oxide derivatives of long chainedcarboxylic acids, such as lauric acid, myristic acid, palmitic acid,oleic acid, or mixtures of acids, such as those found in tall oil,containing from 6 to 60 oxyethylene units; ethylene oxide condensates oflong chained alcohols such as octyl, decyl, lauryl, or cetyl alcohols,containing from 6 to 60 oxyethylene units; and block copolymers ofethylene oxide sections combined with one or more hydrophobic propyleneoxide sections. High molecular weight polymers, such as hydroxyethylcellulose, methyl cellulose, and polyvinyl alcohol, are also usable.

In a preferred embodiment of the present invention the dispersed pigmentparticles are further stabilized with certain surfactants prior to theintroduction of any monomers used to make the second polymer. Thesesurfactants include the family of sulfosuccinic acid esters of theformula R—OC(O)CH2CH(SO3H)C(O)OR′, where R and R′ may be alkyl, aryl,allyl, vinyl, styrenyl, or (meth)acryl, or H, and where R and R′ may bethe same or different, with the exception that R and R′ may not both beH. Preferably, R is C6 to C16 alkyl and R′ is allyl. It has beendiscovered that use of such surfactants in the manner specified allowsthe emulsion polymerization to be run with much lower gel levels thanresult when no surfactant is used, or when other surfactants are used.

After the emulsion polymerization is complete, the polymer encapsulatedpigment particles may be provided as an aqueous dispersion, oralternately they may be provided as a solid in the form of a powder orpellet. The polymer encapsulated pigment particles may be removed fromthe aqueous medium of the emulsion polymerization by any appropriatetechnique including, for example, evaporative drying, spray drying,filtration, centrifugation, or coagulation. When thepolymer-encapsulated pigment particles are provided as a solid, it ispreferred that the Tg of the second polymer, or the Tg of the outermostphase of the second polymer in the case where the second polymercontains multiple phases, is above the temperature at which thepolymer-encapsulated pigment particles will be stored, transported, andoptionally processed prior to final application.

The composition of the present invention including the opacifyingpigment encapsulated in second polymer of the invention is typically acoating or a plastic. Optionally, the coating or plastic also includesone or more of extender particles, secondary pigment particles, andthird polymers.

The binder of the coating or plastic of the present invention is thecontinuous medium containing the polymer-encapsulated pigment particles.The binder may consist solely of the second polymer which encapsulatesthe pigment particles, or it may be a mixture of the encapsulatingsecond polymer and one or more third polymers. Both the second polymerand third polymer are independently, alternatively a homopolymer, acopolymer, an interpenetrating network polymer, and a blend of two ormore polymers or copolymers. Suitable third polymers include acrylic(co)polymers, vinyl acetate polymers, vinyl/acrylic copolymers,styrene/acrylic copolymers, polyurethanes, polyureas, polyepoxides,polyvinyl chlorides, ethylene/vinyl acetate polymers, styrene/butadienepolymers, polyester polymers, polyethers, and the like, and mixturesthereof.

In one embodiment the binder may be a mixture of a polymer and apre-polymeric material. The polymer-encapsulated pigment particles arealternatively provided in a liquid medium such as an organic solvent orwater, or a mixture of organic solvents and water, or are provided as asolid, such as a powder. The optional third polymer is alternativelyprovided in a liquid medium such as a solution polymer, an emulsionpolymer, or a suspension polymer, or is provided as a solid, such as apolymer powder or an extrusion polymer. Either or both the secondpolymer of the polymer-encapsulated pigment or the optional thirdpolymer may contain reactive groups, which upon formation of a coatingfilm or finished plastic part or afterwards, crosslink either withthemselves or with externally added crosslinkers to provide acrosslinked binder. Examples of pre-polymeric materials areethylenically unsaturated monomers and oligomers, and two-partcrosslinking systems such as compositions containing isocyanate groupsand alcohol groups. Conventional crosslinking agents such as, forexample, polyaziridine, polyisocyanate, polycarbodiimide, polyepoxide,polyaminoplast, polyalkoxysilane, polyoxazoline, polyamine, and apolyvalent metal compound can be used as externally added crosslinkers.Typically, from 0 to 25 wt % of the crosslinking agent is used, based onthe dry weight of the polymer.

The polymers which form the binder typically have glass transitiontemperatures in the range of from −60° C. to 150° C., as calculated bythe Fox equation [Bulletin of the American Physical Society 1, 3 Page123 (1956)]. The coating or plastic composition optionally containscoalescents or plasticizers to provide the polymers with effective filmformation temperatures at or below the temperature at which the coatingis applied or cured, or the plastic part is formed. The level ofoptional coalescent is typically in the range of from 0 to 40 wt %,based on the weight of the polymer solids.

In a preferred embodiment of the present invention, the second polymercontains at least two phases, where-in one second polymer phase has a Tggreater than or equal to 30° C., preferably greater than or equal to 45°C., and at least one other second polymer phase has a Tg less than orequal to 12° C., preferably less than or equal to 0° C., most preferablyless than or equal to −5° C. In this embodiment of the presentinvention, the one second polymer phase may be between 5% and 50%,preferably between 10% and 40%, and most preferably between 15% and 30%,by weight based on the pigment particle weight. The total of the rest ofthe polymer phases of the second polymer can be between 5% and 150%,preferably between 10% and 125%, most preferably between 20% and 100%,by weight based on the pigment particle weight.

In a preferred embodiment of the present invention, the second polymercontains at least two phases, wherein the first second polymer phase tobe polymerized contains a multifunctional monomer to crosslink thatphase. Suitable multifunctional monomers include, as examples, allyl(meth)acrylate, divinyl benzene, ethylene glycol di(meth)acrylate,propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate,glycerol tri(meth)acrylate, and polyethylene glycol di(meth)acrylate.The multifunctional monomer may be present from 0.01% to 50% by weightbased on the total weight of the monomers which make up the first phaseof the second polymer, preferably the multifunctional monomer is 0.1% to10%, more preferably from 0.2% to 5%, most preferably from 0.2% to 2% ofthe first monomer phase. In this embodiment of the present invention, itis preferred that all of the phases of the second polymer have a Tg lessthan or equal to 5° C., preferably less than or equal to −5° C. In thisembodiment of the present invention, the first phase of second polymermay be between 5% and 50%, preferably between 10% and 40%, and mostpreferably between 15% and 30%, by weight based on the pigment particleweight. The total of the rest of the polymer phases of the secondpolymer can be between 5% and 150%, preferably between 10% and 125%,most preferably between 20% and 100%, by weight based on the pigmentparticle weight.

The coating or plastic of this invention optionally contains extenderparticles. The extender particles do not significantly scatter light.Extender particles have an index of refraction of less than 1.8 andtypically greater than or equal to 1.3. Suitable extender particlesinclude calcium carbonate, calcium sulfate, barium sulfate, mica, clay,calcined clay, feldspar, nepheline, syenite, wollastonite, diatomaceousearth, alumina silicates, non-film forming polymer particles, aluminumoxide, silica, and talc. Other examples of extenders include solid beadextenders, also known in the art as solid bead pigments, such aspolystyrene and polyvinyl chloride beads.

The coating or plastic of this invention optionally contains secondarypigment particles. The secondary pigment particles have an index ofrefraction less than the index of refraction of the polymer matrix.Secondary pigment particles include pigment particles containing airvoids, such as polymer particles containing air voids. The air void ischaracterized as having an index of refraction close to or equal to 1.Secondary pigment particles including microsphere pigments such aspolymer particles containing one or more voids and vesiculated polymerparticles are disclosed in U.S. Pat. No. 4,427,835; U.S. Pat. No.4,920,160; U.S. Pat. No. 4,594,363; U.S. Pat. No. 4,469,825; U.S. Pat.No. 4,468,498; U.S. Pat. No. 4,880,842; U.S. Pat. No. 4,985,064; U.S.Pat. No. 5,157,084; U.S. Pat. No. 5,041,464; U.S. Pat. No. 5,036,109;U.S. Pat. No. 5,409,776; and U.S. Pat. No. 5,510,422.

The coating or plastic of this invention contains from 1 to 50 volume %pigment particles in the form of polymer-encapsulated pigment particles,preferably from 3 to 30 volume %, and more preferably from 5 to 20volume %, based on the total volume of the coating or plastic. Thecoating or plastic contains from 10 to 99 volume % second and thirdpolymer, preferably from 20 to 97 volume %, and more preferably from 25to 80 volume %, based on the total volume of the coating or plastic. Thecoating or plastic contains from 0 to 70 volume % extender particles,preferably from 0 to 65 volume %, and more preferably from 0 to 60volume %, based on the total volume of the coating or plastic. Thecoating or plastic contains from 0 to 20 volume % secondary pigmentparticles, preferably from 0 to 17 volume %, and more preferably from 0to 15 volume %, based on the total volume of the coating or plastic.

The coating composition of the present invention optionally may alsoinclude other materials commonly found in coatings such as extenders,other polymers, hollow sphere pigments, solvents, coalescents, wettingagents, defoamers, rheology modifiers, crosslinkers, dyes, pearlescents,adhesion promoters, dispersants, leveling agents, optical brighteners,ultraviolet stabilizers, preservatives, biocides, and antioxidants.

Examples of “coatings” herein include inks, paper coatings;architectural coatings, such as interior and exterior house paints, woodcoatings and metal coatings; coatings for leather; coatings andsaturants for textiles and nonwovens; adhesives; powder coatings; andtraffic paints such as those paints used to mark roads, pavements, andrunways. Liquid coatings may be water or solvent based. When the coatingis a powder coating, it is preferred that the Tg of the polymericmatrix, or the Tg of the outer most phase of the polymeric matrix in thecase where the polymeric matrix contains multiple phases, is above thetemperature at which the coating will be stored, transported, andoptionally processed prior to final application. When the coating is asolvent-based coating, it is preferred that the second polymer of thepolymer-encapsulated pigment particles is not substantially soluble inthe solvent or mixture of solvents utilized in the coating.

The plastic of the present invention optionally may also include othermaterials commonly found in plastics such as pigment particles which donot fall under the present invention, extenders, other polymers, hollowsphere pigments, plasticizers, flow agents, and crosslinkers. “Plastics”herein includes solid or flexible materials in the form of objects,films, etc.

The examples which follow illustrate aspects of the present invention.The abbreviation “g” represents “grams”. The abbreviation “mm”represents “millimeters”. The abbreviation “cm” represents“centimeters”. The abbreviation “mil” represents “ 1/1000ths of aninch”.

ABBREVIATIONS

SDS=Sodium dodecylbenzene sulfonate (23%)SSS=Sodium styrene sulfonateTREM™ LF-40=Sodium dodecyl allyl sulfosuccinate (40%)t-BHP=t-Butyl hydroperoxideAIBN=azoisobutyronitrileSSF=Sodium sulfoxylate formaldehydeIAA=Isoascorbic acidEDTA=Ethylene diamine tetra acetic acid sodium salt (VERSENE™)nDDM=n-dodecylmercaptanBMA=Butyl methacrylateBA=Butyl acrylateMMA=Methyl methacrylateDMAEMA=dimethylamino ethyl methacrylateAMPS™=2-acrylamido-2-methylpropane-sulfonic acid

STY=Styrene

MSi=3-mercaptopropyl trimethoxysilaneMAA=Glacial methacrylic acidSEM=Sulfoethyl methacrylateDI water=Deionized water

EXAMPLE 1 Preparation of Water-Soluble Sulfur Acid-Functional FirstPolymer

A 250 ml flask equipped with a magnetic stirrer, N2-inlet, refluxcondenser, heating mantel, and thermocouple was charged with 20 g ofSEM, 4 g of DMAEMA, 10 g of BA, 16 g of MMA, 1.1 g of nDDM, 0.5 g ofAIBN, and 100 g of n-propanol. The flask was purged with N2, and heatedto 60° C., at which point the heating mantel was turned off and thereaction mixture was allowed to exotherm to 80° C. The heating mantelwas turned back on and the reaction mixture was held at 80° C. for 3hours. The temperature was then raised to 93° C., and 0.25 g of AIBN in2.0 g n-propanol was added. The temperature was held at 93° C. for 1 hr;then the flask was cooled to room temperature. The product was pouredinto 100 ml of hexane, then the solid polymer was collected and dried.The dried polymer was dissolved in sufficient water and NH3 to make a21.3% solution at pH 5.0

EXAMPLE 2 Preparation of Water-Soluble Sulfur Acid-Functional FirstPolymer

A monomer solution was made as 20 g of AMPS™, 4 g of DMAEMA, 10 g of BA,16 g of MMA, 1.1 g of nDDM, 20.66 g of ethanol, and 6.88 g of water. A250 ml flask equipped with a magnetic stirrer, N2-inlet, refluxcondenser, heating mantel, addition funnel, and thermocouple was chargedwith 0.5 g VAZO™52, 27.51 g of the monomer solution, 5.9 g of water, and17.67 g of ethanol. The flask was purged with N2, and heated to 55° C.,at which point the heating mantel was turned off and the reactionmixture was allowed to exotherm to 70° C. The heating mantel was turnedback on and the rest of the monomer solution was added over 30 min whilethe temperature was maintained at 70° C. After the addition of themonomer solution was completed the reaction mixture was held at 70° C.for 0.5 hours. The temperature was then raised to 77° C., and 0.5 g ofVAZO™52 in 1.0 g ethanol was added. The temperature was held at 77° C.for 1 hr, then the flask was cooled to room temperature and the solventwas stripped off. The dried polymer was dissolved in sufficient waterand NH3 to make a 21.0% solution at pH 4.0

EXAMPLE 3 Preparation of Water-Soluble Sulfur Acid-Functional FirstPolymer

To a 1 L 3-neck flask containing 300 g of denatured ethanol, 40 g BA, 90g MMA, and 70 g SEM was added. Then, 4.2 g n-DDM was added via pipette,and 2.72 g VAZO™52 initiator. The combined solution was placed underpositive pressure of nitrogen and heated to 60 C for 4 hours. Afterwhich time 1 g VAZO™52 was added to chase down unreacted monomer. Thereaction was then cooled to room temperature. The solids were determinedby removal of volatiles in a vacuum oven in triplicate, 60.1%. Theproduct was poured into 100 ml of hexane; then the solid polymer wascollected and dried. The dried polymer was dissolved in sufficient waterand NH3 to make a 10% solution at pH 4.0

COMPARATIVE EXAMPLE A Preparation of Sulfur-Acid Functional Polymer

A 1 liter glass reactor was charged with 158.59 g ethanol. Under anitrogen blanket the reactor was heated to 75° C. When the reactorreached 75° C. a monomer feed consisting of 58.83 g ethanol, 2.05 gVAZO™-52, 6.02 g n-DDM, 127.87 g MMA and 22.56 g SEM was fed into thereactor over a period of 2 hours and 52 minutes. A temperature of 75±2°C. was maintained throughout the whole process. At the end of themonomer feed a solution of 1.50 g VAZO™-52 dissolved in 22.58 g ethanolwas fed into the reactor over a period of 28 minutes. At the end of thisfeed the temperature was maintained at 75±2° C. for another 40 minutesbefore cooling. Final solids of the product was 39.7%. The drieddispersant was not water soluble at or below pH 5.

COMPARATIVE EXAMPLE B Preparation of Sulfur-Acid Functional Polymer

A 1 liter glass reactor was charged with 158.59 g ethanol. Under anitrogen blanket the reactor was heated to 75° C. When the reactorreached 75° C., a monomer feed consisting of 58.83 g ethanol, 2.05 gVAZO™-52, 6.02 g n-DDM, 100.79 g MMA, 9.03 g SEM and 40.62 g AA was fedinto the reactor over a period of 2 hours and 52 minutes. A temperatureof 75±2° C. was maintained throughout the whole process. At the end ofthe monomer feed a solution of 1.50 g VAZO™-52 dissolved in 22.58 gethanol was fed into the reactor over a period of 28 minutes. At the endof this feed the temperature was maintained at 75±2° C. for another 40minutes before cooling. Final solids of the product was 40.4%. The drieddispersant was not water soluble at or below pH 5. A water solution ofthe dried dispersant was made by adding sufficient NH3 to neutralize allthe MAA and SEM acid groups; the pH was greater than 6

COMPARATIVE EXAMPLE C Preparation of Non-Sulfur-Acid Polymer

A 250 ml flask equipped with a magnetic stirrer, N2-inlet, refluxcondenser, heating mantel, and thermocouple was charged with 7.75 g MAA,10 g BA, 32.25 g MMA, 1.08 g nDDM, 0.5 g AIBN, and 92.5 g n-propanol.The flask was purged with N2, and heated to 65° C., at which point theheating mantel was turned off and the reaction mixture was allowed toexotherm to 80° C. The heating mantel was turned back on and thereaction mixture was held at 80° C. for 3 hours. The temperature wasthen raised to 93° C., and 0.25 g of AIBN in 2.5 g n-propanol was added.The temperature was held at 93° C. for 1 hr; then the flask was cooledto room temperature. The dried dispersant was not water soluble at orbelow pH 5. To the dried dispersant was added 90.17 grams ofdeionized-water and 20.86 grams ammonia (2.8%). The dispersant formed aclear solution after about 15 minutes stirring at room temperature. Thetheoretical solids of this dispersant solution was 7.5%. The pH wasmeasured to be 9.0

EXAMPLE 4 Formation of Opacifying Pigment Dispersion

A steel grind pot was charged with 31.7 g of Example 1 and 95.2 g water.450 g TiO2 (TIPURE™ R-706) was added slowly while grinding at ˜2000 rpmusing a Premier Mill Corp. Model 50 dispersator equipped with a diskblade. After addition of the TiO2, the slurry was ground for 20 min;then an additional 11.3 g of water was added. The solids were 76.5%.

EXAMPLE 5 Formation of Opacifying Pigment Dispersion

A steel grind pot was charged with 71.6 g of Example 2 and 235.6 gwater. 1000 g TiO2 (TIPURE™ R-706) was added slowly while grinding at˜2000 rpm using a Premier Mill Corp. Model 50 dispersator equipped witha disk blade. After addition of the TiO2 the slurry was ground for 20min. The solids were 76.5%.

EXAMPLE 6 Formation of Opacifying Pigment Dispersion

A steel grind pot was charged with 40.0 g of Example 3 and 41.4 g water.265 g TiO2 (TIPURE™ R-706) was added slowly while grinding at ˜2000 rpmusing a Premier Mill Corp. Model 50 dispersator equipped with a diskblade. After addition of the TiO2 the slurry was ground for 20 min. Thesolids were 76.5%.

COMPARATIVE EXAMPLE D Formation of Opacifying Pigment Dispersion

A stainless steel grind pot was charged with 100.0 g of the aqueoussolution of Comparative Example B and 67.67 g water. At 1000 rpm's 500 gTIPURE™ R-706 was added in about 2 minutes. The agitation was maintainedat 1000 rpm's for 1 hour. The slurry was filtered through a 325 meshfiltration bag. The solids was measured to be 75.5%.

COMPARATIVE EXAMPLE E Formation of Opacifying Pigment Dispersion

A steel grind pot was charged with 37.5 g of Comparative Example C and143.7 g water. 500 g TiO2 (TIPURE™ R-706) was added slowly whilegrinding at ˜2000 rpm using a Premier Mill Corp. Model 50 dispersatorequipped with a disk blade. After addition of the TiO2 the slurry wasground for 20 min. The solids were 73.4%.

EXAMPLE 7 Formation of Polymer-Encapsulated Pigment Particles

A 250 ml, four necked round bottom flask was equipped with paddlestirrer, thermometer, nitrogen inlet, and reflux condenser. 15 g DIwater and 1.2 g SDS was added to the kettle. While kettle contents werestirring, 94.9 g of Example 6 was added to kettle. The kettle was thenheated to 50° C. under a nitrogen atmosphere. A monomer emulsion (ME)was prepared by mixing 7 g DI water, 1.5 g SDS, 20.9 g BMA, 14.4 g MMA,and 0.7 g MAA. With the kettle water at 50° C., 2 g of 0.15% solution inDI water of ferrous sulfate heptahydrate was added to the kettle. Thiswas followed by the feeding in 9.5 g of 4.2% solution in DI water oft-BHP and 3.2% solution in DI water of SSF over 65 minutes. 2 minuteslatter the ME was started and fed to the kettle over a 44 minute periodat 50° C. After the completion of the monomer feed the dispersion washeld at 50° C. until all feeds were finished. The polymer was cooled 25°C. Then the dispersion was neutralized with 1 g of 14% aqua ammonia andthen filtered. Trace amounts of gel were filtered in a 100 mesh filter.

EXAMPLE 8 Formation of Polymer-Encapsulated Pigment Particles

To a 500 ml four neck round bottom flask equipped with paddle stirrer,N2-inlet, reflux condenser, heating mantel, and thermocouple was chargedwith 197.3 g of Example 5 (73.0% solids) along with a solution of 2.5 gSDS mixed in 20 g DI water. The flask was purged with N2, and heated to50° C. With the kettle temperature at 50° C., a solution of 4.0 g of0.1% iron sulfate and 0.4 g of 1% EDTA was added to the reactor. Twominutes later co-feed #1 consisting of 2.0 g t-BHP dissolved in 36 g DIwater and co-feed #2 consisting of 1.1 g SSF dissolved in 36 g DI waterwas fed to the reactor at a rate of 0.3 g/min. Two minutes after thestart of the co-feed solutions, a monomer emulsion (ME 1) preparedpreviously by mixing 5.2 g DI water, 1.25 g SDS, 16.7 g BMA, 11.5 g MMA,and 0.6 g MAA was fed to the reactor at a rate of 2.0 g/min. When ME 1was complete, a second monomer emulsion (ME 2) prepared by mixing 22.8 gDI water, 5.0 g SDS, 66.8 g BA, 47.2 g MMA, and 1.2 g MAA was fed to thereactor at a rate of 2.0 g/min. Upon the completion of the ME 2 feed theco-feeds were continued for another 20 min until completion. Thecontents of the reactor were then cooled to room temperature and 3.0grams of aqua ammonia (14%) was added. The contents of the reactor werethen filtered to remove any gel. The filtered dispersion had a solidscontent of 60.8% with 2.5 grams of dry gel removed.

EXAMPLE 9 Formation of Polymer-Encapsulated Pigment Particles

To a 500 ml four neck round bottom flask equipped with paddle stirrer,N2-inlet, reflux condenser, heating mantel, and thermocouple was chargedwith 188.23 g of Example 5 (76.5% solids) along with a solution of 1.5 gTREM™ LF-40 in 29 g DI water. The flask was purged with N2, and heatedto 50° C. With the kettle temperature at 50° C., a solution of 4.0 g0.1% iron sulfate and 0.4 g 1% EDTA was added to the reactor. Twominutes later co-feed #1 consisting of 2.0 g t-BHP dissolved in 31 g DIwater and co-feed #2 consisting of 1.1 g IAA dissolved in 31 g DI waterwas fed to the reactor at a rate of 0.25 g/min. Two minutes after thestart of the co-feed solutions, a monomer emulsion (ME 1) preparedpreviously by mixing 5.2 g DI water, 1.25 g SDS, 16.7 g BMA, 11.5 g MMA,and 0.6 g MAA was fed to the reactor at a rate of 2.0 g/min. When ME 1was complete, a second monomer emulsion (ME 2) prepared by mixing 22.8 gDI water, 5.0 g SDS, 66.8 g BA, 47.2 g MMA, and 1.2 g MAA was fed to thereactor at a rate of 2.0 g/min. Upon the completion of the ME 2 feed theco-feeds were continued for another 20 min until completion. Thecontents of the reactor were then cooled to room temperature and 3.0 gaqua ammonia (14%) was added. The contents of the reactor were thenfiltered to remove any gel. The filtered dispersion had a solids contentof 62.8% with 0.36 grams of dry gel removed.

EXAMPLE 10 Formation of Polymer-Encapsulated Pigment Particles

A 500 ml, four necked round bottom flask was equipped with paddlestirrer, thermometer, nitrogen inlet, and reflux condenser. 30 g of DIwater was added to the kettle. While kettle content was stirring, 197.3g of 76.5% solids Example 5 was added to kettle. The kettle was thenheated to 50° C. under a nitrogen atmosphere. A monomer emulsion #1(ME#1) was prepared by mixing 5 g DI water, 1.3 g SDS, 16.7 g BMA, 10.2g MMA, and 1.4 g SSS. A second monomer emulsion (ME#2) was prepared bymixing 22 g DI water, 5 g SDS, 66.8 g BA, and 48.4 g MMA. With thekettle water at 50° C., 4 g of 0.15% solution in DI water of ferroussulfate heptahydrate was added to the kettle along with 0.4 g of a 1%solution in DI water of VERSENE™. This was followed by the feeding in 38g of 3.7% solution in DI water of t-BHP and 37.1 g of 3% solution in DIwater of IAA over 100 minutes. 2 minutes latter the ME#1 was started andfed to the kettle over 18 minute period at 50° C. After the completionof ME#1, ME#2 was started. ME#2 was fed in over 75 minutes. Thedispersion was held at 50° C. until all feeds were finished. Sample wasthen cooled to 25° C. and 4 g of a 14% solution in DI water of aquaammonia was added. The sample was then filtered through 100 mesh filter.0.015 g of gel was collected.

EXAMPLE 11 Formation of Polymer-Encapsulated Pigment Particles

A 500 ml, four necked round bottom flask was equipped with paddlestirrer, thermometer, nitrogen inlet, and reflux condenser. 25 g DIwater was added to the kettle. While kettle content was stirring, 194.9g of 73.9% solids Example 5 was added to kettle. The kettle was thenheated to 50° C. under a nitrogen atmosphere. A monomer emulsion #1(ME#1) was prepared by mixing 10 g DI water, 1.3 g SDS, 16.7 g BMA, 11.3g MMA, and 0.3 g SSS. A second monomer emulsion (ME#2) was prepared bymixing 22 g DI water, 5 g SDS, 66.8 g BA, 47.2 g MMA and 1.2 g SSS. Withthe kettle water at 50° C., 4 g of 0.15% solution in DI water of ferroussulfate heptahydrate was added to the kettle along with 0.4 g of 1%solution in DI water of VERSENE™. This was followed by the feeding in 38g of 3.7% solution in DI water of t-BHP and 37.1 g of 3% solution in DIwater of IAA over 100 minutes. 2 minutes latter the ME#1 was started andfed to the kettle over 18 minute period at 50° C. After the completionME#1, ME#2 was started. ME#2 was fed in over 75 minutes. The dispersionwas held at 50° C. until all feeds were finished. Sample was then cooledto 25° C. and 4 g of a 14% solution in DI water of aqua ammonia wasadded. The sample was then filtered through 100 mesh filter. 0.13 g ofgel was collected.

Comp. Example F Formation of Polymer-Encapsulated Pigment Particles

A 1 liter reactor was charged with 233.0 g DI water and 6.3 g TRITON™X-405 (35% solids). Under agitation 290.0 g of the TiO2 slurry Comp.Example D was slowly added to the reactor. Under a nitrogen atmospherethe reactor was heated to 50° C. When the reactor reached 50° C. a feedof 0.87 g SSF dissolved in 26.1 g DI water was started simultaneous witha feed of 1.58 g tBHP (70% active) dissolved in 24.5 g DI water. Bothfeeds were set to run for 4 hours and 5 minutes. After 5 minutes intothe feed, a mixture of 4.5 g FeSO4 (0.1% solids) and 11.0 g VERSENE™ (1%solids) were added to the reactor and a pre-emulsified monomer feed wasstarted consisting of 28.8 g DI water, 4.8 g DS-4 (23%), 43.7 g MMA,63.5 g BMA and 2.2 g MAA. The pre-emulsified monomer feed was set to runfor 3.5 hours. After about 1 hour and 12 minutes into the monomer feed,massive amounts of sediment formed rendering agitation impossible. Thebatch was abandoned.

Comp. Example G Formation of Polymer-Encapsulated Pigment Particles

To a 250 ml four neck round bottom flask equipped with paddle stirrer,N2-inlet, reflux condenser, heating mantel, and thermocouple werecharged with 98.09 g of Comp. Example E (73.4% solids). A solution of1.2 g SDS mixed in 15 g DI water was also added to the flask. The flaskwas purged with N2, and heated to 50° C. With the kettle temperature at50° C., a solution of 2.0 g of 0.1% iron sulfate was added to thereactor. Two minutes later co-feed #1 consisting of 0.5 g t-BHPdissolved in 9 g DI water, and co-feed #2 consisting of 0.28 g of SSFdissolved in 9 g DI water was fed to the reactor at a rate of 0.15g/min. Two minutes after the start of the co-feed solutions, a monomeremulsion (ME) prepared previously by mixing 7.0 g DI water, 1.45 g SDS,20.9 g BMA, 14.4 g MMA, and 0.7 g MAA was fed to the reactor at a rateof 1.0 g/min. After five minutes of feeding the ME, the batch had to beaborted due to a massive amount of coagulation in the reactor.

EXAMPLE 11 Formation of Polymer-Encapsulated Pigment Particles

To a 500 ml four neck round bottom flask equipped with paddle stirrer,N2-inlet, reflux condenser, heating mantel, and thermocouple was chargedwith 188.23 g of Example 5 (73.0% solids) along with a solution of 2.5 gSDS mixed in 20 g DI water. The flask was purged with N2, and heated to50° C. With the kettle temperature at 50° C., a solution of 4.0 g of0.1% iron sulfate and 0.4 g of 1% EDTA was added to the reactor. Twominutes later co-feed #1 consisting of 2.0 g t-BHP dissolved in 36 g DIwater, and co-feed #2 consisting of 1.1 g IAA dissolved in 36 g DI waterwas fed to the reactor at a rate of 0.3 g/min. Two minutes after thestart of the co-feed solutions, a monomer emulsion (ME 1) preparedpreviously by mixing 5.2 g DI water, 1.25 g SDS, 16.7 g BMA, 11.5 g MMA,and 0.6 g MAA was fed to the reactor at a rate of 2.0 g/min. When ME 1was complete, a previously prepared second monomer emulsion (ME 2)consisting of 22.8 g DI water, 5.0 g SDS, 66.8 g BA, and 47.2 g MMA wasdivided in half. Seventy-one g of ME 2 (designated ME 2 B), was removedand set aside. To the remaining one half of ME 2 was added 1.2 g MAA(designated ME 2 A). ME 2 A was fed to the reactor at a rate of 2.0g/min. Upon completion of the ME 2 A feed, ME 2 B was fed to the reactorat a rate of 2.0 g/min. Five minutes after the start of ME 2 B, 3.0 gaqua ammonia (14%) was added to the kettle. Upon the completion of theME 2 B feed the co-feeds were continued for another 20 min untilcompletion. The contents of the reactor were then cooled to roomtemperature and filtered to remove any gel. The filtered dispersion hada solids content of 61.0% with 0.04 grams of dry gel removed.

1. An opacifying pigment encapsulated in polymer comprising: a pigmentparticle having an average particle diameter of from 150 nm to 500 nmand an index of refraction of at least 1.8; from 0.1% to 25% by weight,based on the weight of said pigment particle, water-soluble sulfuracid-functional first polymer; and from 10% to 200%, by weight, based onthe weight of said pigment particle, second polymer that at leastpartially encapsulates said pigment particle.
 2. The opacifying pigmentencapsulated in polymer of claim 1 wherein said sulfur acid-functionalfirst polymer comprises at least two amine moieties.
 3. The opacifyingpigment encapsulated in polymer of claim 1 or claim 2 wherein saidsecond polymer comprises, as a copolymerized unit, at least oneacid-functional monomer.
 4. The opacifying pigment encapsulated inpolymer of claim 1 or claim 2 wherein said second polymer comprises atleast two phases, wherein one polymer phase has a Tg greater than orequal to 40° C. and one polymer phase has a Tg less than or equal to 25°C.
 5. The opacifying pigment encapsulated in polymer of claim 1 or claim2 wherein said second polymer comprises at least two phases, wherein thefirst polymer phase includes at least one multifunctional monomer. 6.The opacifying pigment encapsulated in polymer of claim 1 or claim 2wherein said pigment particle comprises TiO2.
 7. The opacifying pigmentencapsulated in polymer of claim 3 wherein said acid-functional monomeris a sulfur acid-functional monomer.
 8. A process for forming anopacifying pigment encapsulated in polymer comprising: (a) dispersing apigment particle having an average particle diameter of from 150 nm to500 nm and an index of refraction of at least 1.8 in a medium with from0.1% to 25% by weight, based on the weight of said pigment particle,water-soluble sulfur acid-functional first polymer; and (b) performingan emulsion polymerization in the presence of said dispersed pigmentparticle to provide from 10% to 200%, by weight, based on the weight ofsaid pigment particle, second polymer that at least partiallyencapsulates said dispersed pigment particle.
 9. The process of claim 8wherein said sulfur acid-functional first polymer comprises at least twoamine moieties
 10. The process of claim 8 wherein said second polymercomprises, as a copolymerized unit, at least one acid-functionalmonomer.
 11. The process of claim 8 wherein said second polymercomprises at least two phases, wherein the first polymer phase formedhas a Tg greater than or equal to 30° C. and one polymer phase has a Tgless than or equal to 12° C.
 12. The process of claim 8 in which saiddispersed pigment particle further comprises at least one surfactantselected from the group consisting of sulfosuccinic acid esters of theformula R—OC(O)CH2CH(SO3H)C(O)OR′, where R and R′ may be alkyl, aryl,allyl, vinyl, styrenyl, or (meth)acryl, or H, and where R and R′ may bethe same or different, with the exception that R and R′ may not both beH, prior to performing said emulsion polymerization to form said secondpolymer.
 13. The process of claim 8 wherein said pigment particlecomprises TiO2.
 14. The process of claim 10 wherein said acid-functionalmonomer is a sulfur acid-functional monomer.
 15. The process of claim 8wherein said second polymer comprises at least two phases, wherein thefirst polymer phase includes at least one multifunctional monomer.
 16. Acomposition comprising said opacifying pigment encapsulated in polymerformed by the process of claim 8.